The present invention relates generally to plasma processing using plasma generated from the microwaves, and more particularly to cooling of a dielectric that transmits the microwaves into a plasma process chamber and maintains the reduced pressure or vacuum environment in the plasma process chamber.
A manufacture of semiconductor devices that forms devices on a semiconductor single crystal substrate (“substrate”), such as silicon, includes the steps of applying photosensitive resin onto a substrate surface using a coater, exposing and transferring a pattern on a previously prepared mask (reticle) using an exposure apparatus, and developing the resultant substrate using a developing machine, thereby obtaining a desired transfer pattern of photosensitive resin. This transfer pattern is used as a mask for subsequent steps of etching, diffusion, film formation, etc., so as to perform a desired process for a substrate, etc., and form devices.
The semiconductor process step inevitably requires a plasma processing apparatus having a high processing speed and damage resistance for improved productivity. A method that introduces the microwaves into dielectric through slots in a metal plate and generates high-density plasma on a dielectric surface at the vacuum side, have recently been proposed as a means to achieve required high processing speed and damage resistance.
A conventional plasma processing apparatus typically supplies the microwaves from a microwave source to a plasma process chamber that accommodates a semiconductor substrate as an object to be processed, through a metal plate having slots and a dielectric. The plasma process chamber is maintained in the reduced pressure or vacuum environment, and supplied with reaction gases. The reaction gases turn into highly active radials and ions by plasma, and react with and plasma-process the semiconductor substrate. The dielectric serves to transmit the microwaves to the plasma process chamber, and maintain the reduced pressure or vacuum environment in the plasma process chamber. The metal plate serves to introduce the microwaves into the dielectric through its slots, prevent the dielectric from liberating and mixing as impurities with the gases, and make the plasma distribution uniform. Such a plasma processing method can generate microwave induced high-density plasma on the dielectric surface at the vacuum side, and is promising method for generating high-density plasma in a large area.
However, the conventional plasma processing method has been disadvantageous in that the dielectric becomes high temperature due to the received heat during the plasma generation. This temperature rise of the dielectric and the lowered temperature just after the apparatus becomes idle, fluctuate process characteristics, and cause malfunctions of the apparatus.
The process characteristics include, for example, the following disadvantages: Photoresist forms a hard layer as a degenerated surface after high-concentration ion implantation, and thus a phenomenon that pops resist, i.e., “popping” occurs when the wafer is heated above the resist bake temperature after the lithography step. The popping resist due to heating remains on the wafer even after over ashing, and greatly affects the remaining chip yield. Therefore, ashing after the high-concentration ion implantation should be processed by maintaining the wafer temperature below the resist bake temperature after the lithography step. In the process using an apparatus that does not have a temperature control function over the dielectric, the dielectric temperature rises whenever the above process step repeats, and the processed wafer becomes above the resist bake temperature due to the radiation heat from the dielectric after the lithography step, whereby the popping occurs disadvantageously.
On the other hand, the apparatus includes, for example, the following malfunctions: The vacuum processing apparatus that uses the dielectric employs a sealer between the dielectric and a process-chamber component to maintain the vacuum against the outside. In general, this sealer utilizes a fluororubber system sealer, a perfluoro system elastomeric sealer etc., but the highest service temperature is below 200° C. due to the physical properties of the material. Therefore, in the apparatus that does not use a temperature control function over the dielectric, the dielectric temperature rises whenever the process repeats, the dielectric temperature rises above the highest service temperature of the sealer, and the sealer cannot serve to maintain the vacuum. In addition, when the apparatus that does not have a temperature control function of the dielectric is used after long idling, the dielectric and an inner wall of a dielectric holder are below the temperature at which sublimate generated from the processed wafer and reaction products turns from gas to solid, and thus will suffer from depositions since they are not exhausted in the gas state. The reattachment of the cumulative deposition to the processed wafer would greatly lower the chip yield.